1. Field of the Invention
The present invention relates to a cathode ray tube and particularly, to a cathode ray tube, capable of degrading doming effect of a shadow mask and improving performance in press molding of the shadow mask.
2. Description of the Background Art
Generally, a cathode ray tube is a device for converting an electric signal into an electric beam and optically implementing a screen by emitting the electron beam on a fluorescent surface. The device is excellent in displaying quality for a price and accordingly it is widely used.
The cathode ray tube will be described with reference to the accompanied drawings.
FIG. 1 is a schematic view showing an example of a cathode ray tube.
As shown in FIG. 1, the cathode ray tube includes a panel 3 which is a front glass, a funnel 2 which is a rear glass for forming a vacuous space while being combined with the panel 3, a fluorescent surface 13 for functioning as a luminescent material while being coated on an inner surface of the panel 3, an electron gun 6 through which an electron beam 5 for emitting the fluorescent surface 13, a deflection yoke 7 for deflecting the electron beam 5 to the fluorescent surface 13 being mounted in a separated position on an outer circumferential surface of the funnel 2 at a predetermined interval, a shadow mask 8 which is installed in a predetermined interval from the fluorescent surface 13, a mask frame 9 for fixing/supporting the shadow mask 8 and an inner shield 10 which is installed in an extended shape from the panel 3 to the funnel 2, for preventing color purity from being inferior by a magnetic effect by shielding an outer terrestrial magnetism.
Also, in an inner side of the panel 3, a spring supporter 14 in which a supporting spring for elastically supporting the mask frame 9 on the panel 3 is fixed is mounted, a reinforcing band 12 for dispersing a stress generated in the panel 3 and the funnel 2 is installed at an outer side circumference of the panel 3.
As shown in FIG. 2, the shadow mask 8 is a device for sorting colors so that an electron beam 5 emitted from the electron gun 6 can selectively blow a fluorescent surface which is coated on the panel 3, and it includes a effective portion 17 having a plurality of electron beam through holes 15 at the center, a ineffective portion 19 which is formed at the circumference of the effective portion 17 without having the electron beam through hole 15, and a skirt portion 21 which is formed at the circumference of the non-effective portion 19 and is fixed on the mask frame 9.
On one surface of the skirt portion 21 of the shadow mask 8, a guiding notch 18 in which a guiding pin (not shown) of a press device (not shown) for deciding the standard position of the shadow mask in press molding for forming a surface of the shadow mask 8 and the skirt portion 21 is formed.
Here, the guiding pin prevents deflection and rotation of the shadow mask 8 in press molding of the shadow mask 8 and the shape is different according to models of the shadow mask and manufacturers.
Therefore, the guiding notch 18 is formed to match the diameter of the respective guiding pins, and is selectively formed on several sides among four sides of the skirt portion 21 of the shadow mask 8.
On the other hand, the shadow mask 8 is positioned adjacent to the fluorescent surface 13 of the panel 3 as the skirt portion 21 is welded and fixed on the side surface of the mask frame 9 in a spot welding method and the like and the mask frame 9 is fixed on the panel 3.
The conventional cathode ray tube with the above structure implements a screen as the electron beam 5 is deflected by the deflection yoke 7, passes through a plurality of electron beam through holes 15 which are formed in the shadow mask 8 and landed on the fluorescent surface 13 formed on the inner surface of the panel 3, and each luminescent material of the fluorescent surface 13 emits light.
At this time, part of the electron beam 5 impinges on the shadow mask 8 without passing through the electron beam through hole 15, and high heat is generated in the shadow mask 8 by impingement of the electron beam 5.
Therefore, the shadow mask 8 gradually becomes deformed by heat, and this is called as a doming effect.
Since the doming effect changes the position of the electron beam through holes 15, miss-landing that the electron beam can not land on an appropriate fluorescent material, and a color bleed is displayed on the screen. Therefore, a color bleed is generated by a small amount of doming effect since the electron beam through hole is very fine.
The doming effect is generated by thermal expansion of the shadow mask 8 due to the impingement of the electron beam 5 and by deformation of the shadow mask by thermal expansion of the mask frame 9 occurred as the heat generated by the impingement of the electron beam 5 is transferred to the mask frame 9. Such doming effect will be described with reference to FIGS. 3A, 3B and 4.
FIG. 3A is a schematic view showing a doming effect of a shadow mask of the conventional cathode ray tube, FIG. 3B is a schematic view showing a doming effect of a shadow mask caused by thermal expansion of a mask frame of the conventional cathode ray tube, and FIG. 4 is graph roughly showing a doming effect in FIGS. 3A and 3B.
That is, as shown in FIG. 3A, at a moment that a power is applied to the cathode ray tube, part of the electron beam impinges on the shadow mask 8 and the shadow mask 8 is heated and expanded by heat at temperature of 80xcx9c100xc2x0 C. generated by the above impingement.
Therefore, the electron beam through hole 15 of the shadow mask 8 is displaced as a predetermined distance, and the landing position of the electron beam 5 is displaced as xcex94A.
In this case, a miss-landing that the electron beam can not landed on an appropriate fluorescent surface 13 is occurred, and by the miss-landing of the electron beam 5a, color purity of the screen is degraded.
On the other hand, heat generated in the shadow mask 5a is gradually transferred to the mask frame 9, and heat transferred to the mask frame 9 expands the mask frame 9. Therefore, the expanding mask frame 9b pulls the heated and expanded shadow mask 8a. 
That is, as shown in FIG. 3B, the surface of the shadow mask 8b is deformed by expansion of the mask frame 9b and the position of the electron beam through hole 15 is displaced.
Therefore, the landing position of the electron beam 5 is displaced as xcex94B by displacement of the electron beam through hole 15, and accordingly, miss-landing that the electron beam 5b can not land on an appropriate fluorescent surface 13 is occurred, thus to degrade color purity of the screen by miss-landing of the electron beam 5b. 
On the other hand, as shown in FIG. 4, a miss-landing amount xcex94B generated by the doming effect of the shadow mask 8 caused by thermal expansion of the mask frame 9 is larger than the miss-landing amount xcex94A which is generated by the doming effect caused by thermal expansion of the shadow mask 8, and the miss-landing directions are different.
Also, the miss-landing phenomenon (A) by thermal expansion of the mask frame 9 is generated for a longer time than that of the miss-landing phenomenon (B) caused by thermal expansion of the shadow mask, and the miss-landing phenomenon (A) affects more on quality degradation of the cathode ray tube.
That is, doming effect of the shadow mask 8 caused by thermal expansion of the mask frame 9 affects more on degradation of performance of matching landing of the electron beam in manufacturing the cathode ray tube and color purity of the screen than the initial doming effect which is generated by thermal expansion of the shadow mask 8.
The doming effect of the shadow mask caused by thermal expansion of the mask frame 9 is generated as the heated and expanded mask frame 9 pulls the skirt portion 21 of the shadow mask 8. As shown in FIG. 5, a portion where a force that the mask frame 9 pulls the shadow mask 8 is adjacent from the welding spot (portion indicated with oblique lines) of the mask frame 9 and shadow mask 8, and the direction of the force that the mask frame 9 pulls the shadow mask 8 is same as the direction of an arrow shown in FIG. 5.
On the other hand, to reduce the doming effect, the supporting spring 11 which is positioned between the mask frame 9 and the panel 3 for reducing thermal expansion of the mask frame 9 can be composed of two materials having different thermal expansion coefficients, but in case such supporting spring composed of different materials is used, cost of materials was increased.
Therefore, an object of the present invention is to provide a shadow mask of a cathode ray tube capable of reducing doming effect of the shadow mask by adjusting the shape of a guiding notch in which a guiding pin for matching the standard of the shadow mask in press molding of the shadow mask, and improving performance in press molding of the shadow mask.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a cathode ray tube including a shadow mask which is composed of a effective portion having a plurality of holes through which an electron beam passes and a skirt portion extended approximately in a perpendicular direction to the effective portion, wherein a guiding notch is formed in the skirt portion, the guiding notch includes an end portion which is formed to be opened to the end of the skirt portion and a fixing portion to which a guiding means is fixed, and a width of the end portion is wider than the diameter of the fixing portion.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.